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MicroStep Motor Controller

The SIL MicroStep system allows distributed control of up to 16 individual stepper motors. Control signals are sent via Ethernet to the system, which appears as a standard EPICS input/output controller (IOC). In addition to sending control signals to each motor, position and monitoring information may be sent back to the control system.

Developed at the University of Saskatchewan for use in the Canadian Light Source (CLS), the MicroStep design was licensed to SIL under a technology transfer agreement. SIL, in partnership with the Saskatchewan Synchrotron Institute (SSI), have worked to improve, manufacture and market the MicroStep System.

The motor control system's main application is a synchrotron or physics laboratory that currently runs EPICS. However, the MicroStep Motor Control System could be used in any setting where a number of individual motors need to be precisely positioned, such as research, industrial or manufacturing operations.

System Overview

A complete motor control system consists of three main enclosures, Controller Subrack and two Driver Subracks. The Controller Subrack is responsible for taking input control signals from the control system and conditioning them for the Driver Subrack, which in turn directly drives the motors. Each subrack is a standard 3U Eurocard rack and requires +12V to +24V DC input power. Control signals are sent via Ethernet to the system, which appears as a standard EPICS input/output controller (IOC).

Controller Sub-rack

The Controller Subrack is designed to connect directly to StepPack or MicroStep motor drivers. When used with MicroStep motor drivers the Controller can remotely enable or disable a motor and engage/release an electromechanical brake. Additionally, the controller is able to monitor motor position using either quadrature shaft encoders or rotary/linear potentiometers.

The components of a Controller Subrack are a Voltage Regulator module, an Embedded Controller module, and an Interface module. An Embedded Controller module may be connected to a maximum of four Interface modules, each of which relay control signals to two Driver modules in the Driver Subrack. There is room in the chassis for one voltage regulator, two Embedded Controller modules and eight Interface modules, allowing for control of up to sixteen motors.

The Interface module provides an interconnection between the Embedded Controller module and the Driver module. Each Interface module can be connected to two MicroStep Driver modules and two feedback potentiometers which may be used to monitor position.

The Voltage Regulator module contains switching regulators which accept +12V to +24V from an external DC power source and provide +5V to the other modules. Front panel status LEDs and test points for measuring the output of each regulator are provided.

Driver Sub-rack

The MicroStep Driver Subrack may contain up to eight Driver modules. Each Driver module receives input from the MicroStep Controller Subrack and can control one motor. The current per winding can be varied from 0.2A to 3.0A in 0.2A increments. Additionally, the number of microsteps per motor step can be set to 16 different values between 1 and 128 on the Driver module. The modules can drive the following types of motors:

Four-lead, two-windingSix-lead, four-windingEight-lead, four-winding

Each MicroStep Driver module takes input control signals and generates the electrical signals to physically move a micro-stepping motor. Additionally, the Driver module passes feedback information, such as position (from an encoder) or mechanical limit status, back to the Control Crate.

A Regulator module, similar to the one in the Controller Subrack, is installed in the center slot of the Driver Crate. The regulator module contains switching regulators which convert the +12V to +24V supply voltage to +5V for the Driver modules. Front panel LEDs indicate the status of the power supplies. Test points for measuring the power supply and regulator voltages are also provided.

Embedded Controller

The workhorse of the Control Subrack is a pair of single board computers based on the Motorola MC68360 micro controller. Each Embedded Controller module communicates with the operator control system over a 10baseT Ethernet connection and is able to receive and pass on control signals to individual motors. The Embedded Controller can also pass diagnostic information back to the control system such as clockwise/counter-clockwise limit switch and over-travel status.